1. Field of the Invention:
This invention relates to an effective process for recovering uranium from a raffinate containing 10 to 100 mg/l of uranium by coprecipitation with large amounts of the hydroxides or phosphates of other heavy metals at low pH. In this case, the term raffinate is the residual phase which forms after acidulating phosphate rock with a mineral acid such as sulfuric, hydrochloric or nitric acid, and then treating the resulting crude acid with an organic solvent.
2. Description of the Prior Art:
The recent, rapid increase in demand for nuclear power generation facilities has prompted a corresponding increase in the demand for uranium, and because of this demand, future shortages of uranium are expected to occur. For this reason, refining of low quality uranium ores, the recovery of uranium from sea water or from waste liquors and other processes are being studied in many countries. In the present practices of the uranium industry, the lower concentration limit of uranium in ore below which it is uneconomical to attempt to extract uranium from ore is about 0.1%.
Presently, uranium containing ores are treated by conventional processes which begin with leaching of the ores with sulfuric acid or sodium carbonate solutions. The leaching step of the processes is followed by concentration of the extract and further refining by ion exchange or solvent extraction techniques. However, great difficulty is encountered when these methods are used to separate small amounts of uranium from large amounts of other metal ions in concentrated mineral acids. Therefore, attempts have been made to develop techniques which are successful in the extraction of uranium from low grade materials. Several techniques have been developed for the separation of uranium from very dilute solutions such as by precipitating uranium complexes from solution by treatment with organic reagents such as oxine or cupferron; by using inorganic absorbents such as titanium hydroxide, ferric hydroxide or the like; by treatment of the solutions with chelating resins; and by treating the dilute solutions with an ionic surface active agent which results in the formation of insoluble uranium compounds through flotation that are separated by bubbling the solution with air. Further, such techniques as ion exchange, solvent extraction and other recovery processes have also been reported. However, none of these processes have been entirely satisfactory.
A need, therefore, continues to exist for a process which is economically and industrially feasible for the separation of uranium from low grade ores or from dilute solutions.